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Metro Ethernet Link - QOS Query



I have the following setup over a metro ethernet cloud and i would like to implement QOS, to ensure a commited bandwidth for voice traffic over data traffic.

<HO> <-----Metro Ethernet Link-------> <----- Provider Cloud ------> <------> < Branch offices >

Presently last mile is over 100/1000 Mbps Ethernet.

Every Branch has its own subscribed bandwidth over the metro ethernet link.

Provider does that rate limiting at his end.

Between the offices data/voiP traffic is happening over this Metro Ethernet cloud.

At Every offices, we would like to block a certain bandwidth for the VOIP traffic alone.

Say out of 20 Mbps subscribe last mile bandwidth, 2 would be Mbps dedicated to VOIP traffic.

The rest of the bandwidth is allocated for the remaining traffic.

Would the following QOS configuration help to acheive this requirement.

Example config for a site which has the last mile subscribed ethernet bandwidth is 20Mbps.

We would like to block 2 mbps out of this link to voip traffic and rest of the bandwidth is available for data


class-map match-all voice

match access-group 101 --( ACL to match the voip traffic)

policy-map qos-policy-metro-voip

class voice

priority percent 10

class class-default



policy-map Metro-map

class class-default

shape average 20000000

service-policy qos-policy-metro-voip

interface FastEthernet0

** Metro ethernet link ***

service-policy output Metro-map

Kindly provide your valuable suggestions on this.

Thanks / Regards


6 Replies 6


Hello VJ,

this should achieve the desired behaviour. The only thing I would consider: use

class-map match-all voice

match protocol rtp audio

Otherwise you might also get Telephone TFTP, etc. traffic in your voip class. Additionally make sure voip signalling is handled correctly.

Regards, Martin

Hi Martin,

Thank you very much for the reply and your suggestion.

Im a regular reader of your Posts and i realy admire your style of replies.

Always very precise and rich in content. I have learned a lot from your posts.

I Wish you all the Best and keep posting those replies, which makes learning a really interesting one for everyone on this Forum.

Thanks / Regards




I'd recommend using

priority bandwidth 2000

Priority percent

syntax is using the interface bandwidth as a calculating base, see

So 10 percent will not give you 2Mbps, I'm afraid.

Best regards,

Milan Kulik


Hello VJ,

It also depends on the model of the switch which is terminating the link... If it is 6500's or other high end switches, LLQ configs done by you would work fine.. even 3750 metro switch would do the job for you.. but if it is any other switch like 3750, 3560 etc, this wont work... You gotta use the "Shaped Round Robin" SRR queues for this and configure bandwidth allocation accordingly... there are a lot of tweaks you can do with the buffers, bandwidth etc using srr-queue MLS config commands... Hope they bring some advance features on the 3750-E or 3560-E series NEWW switches....



Thanks for the update Raj.

Im presently working on drafting configurations based on SRR queues. Will keep you posted on further queries.


Hello Vijay,

all the best for ur configurations... i have sent you a guide which helps you understand better on the mls qos !!! it has really good examples and explanation...hope the doc helps you....


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